Optical-fiber cable having a perforated water blocking element

ABSTRACT

The present invention provides optical-fiber communication cables with an improved water-blocking element that reduces or eliminates microbending caused by the water-swellable particulate powders by employing such water-swellable powders in conjunction with a smooth but perforated compression-resistant carrier tape. The water-blocking element is deployed within optical-fiber buffer tubes to water-block the buffer tubes and to minimize microbending that can occur when water-swellable particulate powders press against optical fibers.

CROSS-REFERENCE TO PRIORITY APPLICATIONS

This application is a division of commonly assigned U.S. patentapplication Ser. No. 12/648,794 for a Perforated Water-Blocking Element(filed Dec. 29, 2009, and published Jul. 1, 2010, as U.S. PatentApplication Publication No. 2010/0166375 Al), now U.S. Patent No.8,891,923, which itself claims the benefit of U.S. Patent ApplicationNo. 61/141,443, for a Perforated Water-Blocking Element (filed Dec. 30,2008). Each of U.S. Patent Application No. 61/141,443, U.S. patentapplication Ser. No. 12/648,794, and U.S. Patent Application PublicationNo. 2010/0166375 A1 is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an optical-fiber cable that includes aperforated water-blocking element.

BACKGROUND

Water-blocking in optical-fiber buffer tubes and fiber optic cablestypically has been accomplished by using petroleum-based filling gels(e.g., grease). By completely filling all of the free space inside abuffer tube that contains an optical fiber or optical-fiber bundle, thefilling gel blocks the ingress of water into the fiber optic cable.

Moreover, being a thixotropic material, the filling gel also tends tomechanically couple the optical fiber(s) to the buffer tube. Suchmechanical coupling prevents the optical fiber(s) from retracting insidethe buffer tube as the buffer tube is processed during manufacturing, asthe cable is installed or otherwise handled in the field, or as thecable is subjected to thermally induced dimensional changes fromenvironmental exposure.

Although relatively effective for controlling cable flooding, thepetroleum-based filling gels are inconvenient during cable repair andoptical-fiber splicing. The use of such gels requires cleaning thepetroleum-based material from optical fibers prior to splicing (andsometimes from equipment and personnel, too), which can be messy andtime consuming. Consequently, using conventional filling greases isoften undesirable.

Various dry-cable designs have been developed to eliminate fillinggreases while providing some water-blocking and coupling functions. Ineither loose tube fiber cables or ribbon cables, a totally dry designeliminates the filling gel from the enclosed buffer tubes. In a totallydry cable, for example, filling gel may be replaced by a water-blockingelement, such as a tape or a yarn carrying a water-swellable material(e.g., water-swellable powder). Water-swellable powders are dry to thetouch and, when bound to a carrier tape or yarn, can be readily removedduring field operations (e.g., splicing).

Optical fibers are sensitive to mechanical loads, which can causeundesirable microbending. Those having ordinary skill in the art knowthat microbending is induced when small stresses are applied along thelength of an optical fiber, perturbing the optical path throughmicroscopically small deflections in the core.

Water-swellable powders consist of finely ground hard particles. Thesize and hardness of such particulates may be sufficient to causemicrobending and optical attenuation in the optical fibers they contact.

Accordingly, there is a need for a more effective solution to dry cabledesign. In particular, there is a need for a grease-free water-blockingelement that reduces microbending losses in optical fibers yeteffectively blocks the longitudinal movement of water inside a fiberoptic cable and its constituent buffer tubes.

SUMMARY

In one aspect, the present optical-fiber cable includes at least onebuffer tube in which an improved water-blocking element at leastpartially surrounds one or more optical fibers. Stated otherwise, thewater-blocking element is positioned between the optical fiber(s) andits surrounding buffer tube, all within a cable jacket (e.g., polymericjacketing). The water-blocking element possesses discrete perforationsof sufficient size and number to promote water movement. Thewater-blocking element typically includes at least one component thatpermits the water-blocking element to maintain its strength andstructural integrity when immersed in water.

In one embodiment, the water-blocking element includes water-swellableparticulate powder bonded to a substantially non-fibrous,compression-resistant carrier tape. The carrier tape is perforated(i.e., defines a plurality of perforations) to promote water transportto the water-swellable particulate powder. The perforated carrier tapeis positioned adjacent to the optical fiber(s) such that thewater-swellable particulate powder is separated from the opticalfiber(s).

In an alternative embodiment, the water-blocking element includeswater-swellable particulate powder disposed (e.g., encapsulated) betweensubstantially non-fibrous, compression-resistant perforated carriertapes.

In another embodiment, the water-blocking element includeswater-swellable particulate powder bonded to a fibrous carrier tape. Thecarrier tape possesses discrete perforations of sufficient size andnumber to promote water transport from the optical fiber(s) to thewater-swellable particulate powder. The perforated fibrous carrier tapeis positioned adjacent to the optical fiber(s) such that thewater-swellable particulate powder is separated from the opticalfiber(s).

In an alternative embodiment, the water-blocking element includeswater-swellable particulate powder disposed (e.g., encapsulated) betweenperforated fibrous carrier tapes.

The foregoing illustrative summary, as well as other exemplaryobjectives and/or advantages of the invention, and the manner in whichthe same are accomplished, are further explained within the followingdetailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a cross-sectional view of a two-layerwater-blocking element according the present invention in whichwater-swellable powder is bonded to a perforated carrier tape.

FIG. 2 schematically depicts a cross-sectional view of a three-layerwater-blocking element according the present invention in whichwater-swellable powder is disposed between two perforated carrier tapes.

FIG. 3 schematically depicts a top view of an exemplary perforatedcarrier tape according to the present invention.

DETAILED DESCRIPTION

The present invention, which embraces an improved, dry optical-fibercable possessing water-blocking capabilities, is described herein withreference to the accompanying drawings. As will be appreciated by thosehaving ordinary skill in the art, these drawings are schematicrepresentations, which are not necessarily drawn to scale. Thisinvention may be embodied in many different forms and should not beconstrued as limited to the exemplary embodiments set forth herein. Theembodiments disclosed are provided to convey the scope of the inventionto those having skill in the relevant art.

That said, FIG. 1 schematically depicts a water-blocking element (10)formed from an elongate material. The water-blocking element (10) is atwo-layer structure having water-swellable particulate powder (14)bonded (e.g., with an adhesive material) to a carrier tape (16),typically a relatively smooth carrier tape. The carrier tape (16)defines a plurality of perforations (12).

The water-blocking element is positioned within an optical-fiber cablebetween the optical fiber(s) and the buffer tube. The water-blockingelement (10) at least partially encloses the optical fiber(s). Thewater-blocking element (10) is oriented within the buffer tube such thatthe perforated carrier tape (16) is positioned adjacent to the opticalfiber(s), and the water-swellable particulate powder (14) is positionedopposite the optical fiber(s).

The perforations (12) in the carrier tape (16) facilitate the transportof water toward the water-swellable particulate powder (14), therebyactivating the water-blocking characteristics of the water-swellableparticulate powder (14).

As the water-swellable particulate powder (14) swells, the perforations(12) in the carrier tape (16) allow the expanded water-swellableparticulate powders to exude through the perforations (12) of thecarrier tape (16) and into the cavities and interstices surrounding theoptical fiber(s).

The perforations (12) may be of any suitable profile (i.e., size, shape,and/or pattern) so long as the perforations (12) can effectivelytransport water toward the water-swellable particulate powder (14) and,thereafter, can accommodate the expansion of the activatedwater-swellable particulate powders (14). In this regard, although FIG.1 depicts the perforations (12) as holes, other profiles, such as slitsor flaps, are within the scope of the present invention. The use offlaps or slits, instead of holes, may further improve the smoothness ofthe carrier tape.

FIG. 2 schematically depicts a cross-sectional view of anotherembodiment of a perforated water-blocking element (20) according to thepresent invention. The water-blocking element (20) is a three-layerstructure that includes a water-swellable particulate powder layer (24)encapsulated between two carrier tapes (26, 28). The water-swellableparticulate powder (24) is bound (e.g., with an adhesive material) to atleast one (and typically both) carrier tape layers (26, 28).

The two carrier tape layers (26, 28) each have perforations (22) that,as noted, can be of any suitable size, shape, and/or pattern. Theperforations facilitate the transport of incoming water toward thewater-swellable particulate powder (24) and allow the activatedwater-swellable particulate powders (24) to exude through theperforations of the carrier tape (26) that is positioned adjacent to theoptical fiber(s) and into the cavities and interstices surrounding theoptical fiber(s). Moreover, the carrier tape may be coated with awetting agent (e.g., a surfactant) that promotes the transport ofintruding water toward the water-swellable particulate powder. Forexample, a surfactant may reduce the surface tension of at least aportion of the carrier tape so that water can easily move through aperforation toward the water-swellable particulate powder.

As schematically depicted in FIG. 2, the respective perforations incarrier tape layer 26 and carrier tape layer 28 are aligned. Thisembodiment of the present invention, however, is not so limited (i.e.,the respective perforations in the two carrier tape layers need not becoextensive in size, shape, or number). Indeed, it is within the scopeof the invention to employ the second carrier tape layer 28 (i.e., thetape layer nearest the buffer tube wall) with few perforations, if any.

FIG. 3 schematically depicts a top view of an exemplary perforatedcarrier tape according to the present invention having a representativeperforation pattern.

As further discussed herein, the perforated carrier tapes as depicted inFIGS. 1-3 can be formed from either (i) non-fibrous films or sheets or(ii) fibrous fabrics or webs (e.g., nonwovens). In either case, awater-blocking element's perforated carrier tape is typicallywater-insoluble such that it maintains its strength and structuralintegrity when immersed in water.

The water-blocking element according to the present invention isdisposed within the buffer tube in such a way as to surround the opticalfiber(s). The width of the water-blocking element is typically the sameas the inner circumference of the buffer tube. In some embodiments,however, the width of the water-blocking element is at least about tenpercent greater than the buffer tube's inner circumference.

The water-blocking element is typically positioned directly adjacent tothe inner wall of the buffer tube such that there is little, if any,unfilled space between the inner wall of the buffer tube and thewater-blocking element. Otherwise, such unfilled space would allow waterwithin the buffer tube to migrate longitudinally along the buffer tube'sinner wall. The water-blocking element may be secured to the buffertube, for example, using an adhesive, by melt-bonding part of the waterblocking element to the buffer tube during extrusion, or by frictionalcoupling of the water-blocking element and the buffer tube. Suitabletechniques for securing buffer-tube elements (e.g., via adhesives) aredisclosed in commonly assigned U.S. Pat. No. 7,515,795 for aWater-Swellable Tape, Adhesive-Backed for Coupling When Used Inside aBuffer Tube, which is hereby incorporated by reference in its entirety.

The perforated water-blocking element of the present invention providesimproved water-blocking within the buffer tube. If water intrusion(e.g., flooding) does occur, water tends to migrate radially inwardtoward the optical fibers (i.e., the optical-fiber element) containedwithin the buffer tube. In this way, the water-blocking element helps toprevent transport of the water along the length of the optical-fibercable.

Some unfilled space is usually provided adjacent the optical fibers(i.e., between the optical fibers and the perforated carrier tape). Inthis regard, free space, or so-called annular free space, between theoptical fibers and the perforated carrier tape within the buffer tubeallows the optical fibers to move more or less freely within the cable.For example, although the glass fibers and the polymeric buffer tube mayrespond differently to temperature changes, the optical fibers are notfixedly secured to the water-blocking element. Consequently, the opticalfibers are not forced to move as the buffer tube thermally expands orcontracts.

Moreover, as used herein in this context, the term “annular free space”is intended to characterize unfilled space that can exist between theoptical-fiber element (i.e., the optical fibers) and its surroundingstructure (i.e., around the entire perimeter of the optical-fiberelement) regardless of the respective shapes of the optical-fiber cableand its components (e.g., a rectangular ribbon stack within a roundbuffer tube). In this regard, the term “annular free space” as usedherein is not limited to the regular gap between two concentric tubes(or casings) having circular cross-sections (i.e., a perfect annulus).

The structure of the water-blocking element inhibits the drywater-swellable particulate powder from directly contacting the opticalfiber(s). Contact between the optical fiber(s) and the drywater-swellable particulate powder (i.e., before its activation) couldcause microbending in the optical fibers. In other words, the perforatedcarrier tape acts as a barrier between the inactivated water-swellableparticulate powder and the optical fibers.

That said, it is within the scope of the present invention to furtherinclude a coupling material between the optical fibers and theperforated carrier tape of the water-blocking element. Those havingordinary skill in the art will appreciate that to facilitate thetransport of water through the perforated carrier tape to thewater-swellable particulate powder (and thereby activating thewater-blocking characteristics of the water-swellable particulatepowder), the coupling material may be discontinuously provided upon thesurface of the perforated carrier tape.

An exemplary coupling material is disclosed in commonly assigned U.S.Patent Application Publication No. US 2009/0003785 A1 and its relatedU.S. patent application Ser. No. 12/146,588 for a Coupling Compositionfor Optical Fiber Cables, filed Jun. 26, 2008, (Parris et al.).Likewise, the exemplary use of discrete domains of adhesive material tocouple a water-swellable element and optical fibers is disclosed incommonly assigned U.S. Pat. No. 7,599,589 for a Gel-Free Buffer Tubewith Adhesively Coupled Optical Element and commonly assigned U.S. Pat.No. 7,567,739 for a Fiber Optic Cable Having a Water-Swellable Element.Each of these patent publications and patent applications is herebyincorporated by reference in its entirety.

Fibrous, fabric carrier tapes may be employed for water-blockingelements. In one embodiment, for example, the water-swellable,perforated carrier tape of the present invention is a fibrous fabric(e.g., knit, woven, or nonwoven), such as a substrate made fromsynthetic polymeric fibers (e.g., polyester or polyolefin fibers) ornatural fibers (e.g., cellulose). Such fibrous tapes can be surficiallyrough, however, so selecting a suitable, smooth carrier tape should bemade with due consideration. To ensure a smooth surface, fibrous (andnon-fibrous) tapes may be treated with a surface coating formulation(e.g., to achieve a coated paper tape) or otherwise enhanced with athin, smooth film (e.g., a polymeric surface film).

The sensitivity of optical fibers to mechanical loads, as well as thedesire to reduce cable dimensions, makes the use of a smoother carriertape somewhat advantageous. Accordingly, a smooth perforated carriertape may be employed to effectively separate the water-swellableparticulate powder from the optical fibers. This separation helps reducemicrobending and optical attenuation that could otherwise occur if theoptical fiber(s) were to contact the water-swellable particulate powder,such as during cable installation.

Therefore, in a more typical embodiment, a smooth water-swellable,perforated carrier tape is substantially non-fibrous. In exemplaryembodiments, the tape may be a polyester film, such as MYLAR® film, or apolyolefin tape (e.g., polypropylene or polyethylene). Other suitablecarrier tapes include fire-resistant polyimide films (e.g., KAPTON®film).

Whether non-fibrous or fibrous, the carrier tape should yield a reducedoverall thickness of the water-blocking element. In this regard and incontrast to conventional foam inserts, the perforated carrier tape issomewhat resistant to compression (e.g., less bulky). Such reduced bulkpermits the dimensions of the fiber optic cable to be reduced or,alternatively, provides more free space for the optical fibers withinthe buffer tube.

The perforated carrier tape typically possesses Shore A hardness of morethan about 25 (e.g., 30-40), more typically more than about 45 (e.g.,50-60), and most typically more than about 65 (e.g., 70-80 or more).

As used herein, hardness refers to a material's resistance toindentation upon the application of a static load. This is convenientlymeasured using an appropriate Shore durometer (e.g., a Shore Adurometer). The Shore A hardness scale is typically used for softrubbers and the like; the Shore 00 hardness scale is typically used forfoams that have Shore A hardness of less than about 5 (e.g., a Shore 00hardness of less than about 45.) Shore hardness is typically measured atstandard temperature and pressure (STP). As used herein, standardtemperature and pressure (STP) refers to testing conditions of 50percent relative humidity at 70° F. (i.e., about 20° C.) and atmosphericpressure (i.e., 760 torr).

Those having ordinary skill in the art will recognize that for a buffertube having a particular inner diameter, the water-blocking elementshould be thin enough such that the inner diameter of the buffer tube isgreater than the combined thicknesses of all elements within the buffertube. For example, the sum of twice the thickness of the water-blockingelement, and the maximum cross-sectional width of the optical-fiberelement (i.e., the optical fibers) should be less than the innerdiameter of the buffer tube. (Those having ordinary skill in the artwill recognize that the thickness of the water-blocking element isconsidered twice because it typically encircles the optical fibers.) Onthe other hand, the carrier tape must not be too thin or it will tooreadily deform, thereby allowing bumps caused by the water-swellableparticulate powder to be transferred through the carrier tape to theoptical fibers.

The water-swellable particulate powders typically possess a particlesize weight distribution in which the median particle diameter is lessthan about 500 microns, more typically between about 10 and 300 microns.

As will be understood by those familiar with bulk powder measurements,particle size may be measured via light scattering techniques. Forexample, particle sizes and distributions are often characterizedaccording to ASTM B330-2 (“Standard Test Method for Fisher Number ofMetal Powders and Related Compounds”). Alternatively, bulk particlesizes and distributions may be characterized using a Hegman Finenessnumber determined from ASTM D1210-79. Particle-size characterizations ofparticulate powders are described in U.S. Patent Application PublicationNo. US 2008/0274316 A1, which is herein incorporated by reference in itsentirety.

As noted, the size (and size distribution) of the particulates in thewater-swellable powder influence the deformation of the carrier tape.Thus, the size and quantity of the water-swellable particulates must beselected to prevent water-swellable powder “bumps” from causing opticalattenuation (e.g., microbending). In addition, the perforations in thecarrier tape may be sized to obstruct the migration of the drywater-swellable powder through the perforations of the carrier tape(i.e., hinder dry migration of the powder). That said, because thewater-swellable particulate powders are typically bonded (e.g., with anadhesive) to a perforated carrier tape, the perforations need not besmaller (e.g., have a smaller diameter) than the water-swellableparticulate powders to preclude complete or partial passing of theparticulate powders through the perforations. In view of the foregoingand by way of illustration, the perforations typically have a diameterof between about 0.1 millimeter and about 10 millimeters (e.g., betweenabout 0.5 millimeter and about 2 millimeters, such as about 1millimeter).

Exemplary water-swellable materials include a matrix (e.g., ethylenevinyl acetate or rubber) enhanced with about 30 to 70 weight percentsuper absorbent polymers (SAPs), such as particulates of sodiumpolyacrylate, polyacrylate salt, or acrylic acid polymer with sodiumsalt. Such water-swellable materials can be processed on conventionalhot melt adhesive machinery.

As noted, the perforated carrier tapes of the present invention resistsignificant compression, such as that which occurs in foams havingdensity reductions of 30 percent or more. Consequently, the perforatedcarrier tapes are relatively thin, thereby providing more space for theoptical fiber(s) to move within the buffer tube. In other words, aperforated carrier tape itself will provide little coupling between theoptical fiber(s) and the surrounding buffer tubes. In an exemplaryembodiment, the water-blocking element has a perforated carrier tapewith a density of at least about 0.90 g/cm³.

In particular embodiments, the perforated carrier tapes possess onlynegligible compression properties (i.e., a substantially incompressiblematerial).

Therefore, by controlling (i) the particulate size distribution of thewater-swellable powder, along with (ii) the carrier tape parameters(i.e., thickness, strength, hardness, and material), as well as (iii)the carrier tape perforations (i.e., size and quantity), a considerablereduction in optical-fiber microbending, as well as more efficientwater-blocking of the buffer tube is achieved.

As noted, the perforated carrier tapes of the present invention canembrace fibrous carrier tapes (e.g., cellulosic nonwovens), such aspaper or other natural fibers. Perforated fibrous carrier tapes, whichinclude water-swellable particulate powder bonded thereto, arepositioned adjacent to the optical fiber(s) such that thewater-swellable particulate powder is separated from the opticalfiber(s). As such, it is preferable that the fibrous carrier tapesprovide a smooth surface adjacent to the optical fibers.

One exemplary fibrous carrier tape is parchment paper, which is madefrom cellulose, a naturally occurring polymer. As will be understood bythose having ordinary skill in the art, parchment paper may be achievedby treating linear cellulose polymer chains with sulfuric acid. Thisacid treatment promotes cross-linking, thereby providing the parchmentpaper with improved wet strength and water resistance. In addition, someparchment paper (e.g., silicone-coated parchment paper) includes surfacetreatment to further enhance its durability.

As will be understood by those having ordinary skill in the art, fibrouscarrier tapes possess discrete perforations (and inherent interstices)of sufficient size and number to promote water transport from theoptical fiber(s) to the water-swellable particulate powder. In thisregard, the inherent interstices of the fibrous carrier tapes (i.e.,spaces between fibers) occur intrinsically during formation of thefibrous substrate, whereas the larger, discrete perforations are formedin a secondary process (i.e., to achieve the desired distribution ofopenings).

A typical fibrous carrier tape (e.g., a nonwoven) formed from aplurality of polymeric fibers has a polymeric fiber density of more thanabout 80 percent (e.g., 90 percent or more). In other words, the overalldensity of the fibrous carrier tape is at least about 80 percent of thedensity of its constituent polymeric fibers.

* * *

The present water-blocking elements may be included in optical-fibercables and buffer tubes having relatively high filling coefficients andfiber densities. Furthermore, the smoothness of the presentwater-blocking elements facilitates acceptable cable-attenuationperformance.

As used herein, the term “buffer-tube filling coefficient” refers to theratio of the total cross-sectional area of the optical fibers within abuffer tube versus the inner cross-sectional area of that buffer tube(i.e., defined by the inner boundary of the buffer tube). By way ofclarification, the term “buffer-tube filling coefficient” excludesribbon matrix materials (e.g., subunit and common ribbon matrices).

Additionally, as used herein, the term “cumulative buffer-tube fillingcoefficient” refers to the ratio of the total cross-sectional area ofthe optical fibers enclosed within buffer tubes versus the sum of theinner cross-sectional areas of the buffer tubes containing those opticalfibers.

Buffer tubes containing the present water-blocking elements may have abuffer-tube filling coefficient of at least about 0.20, typically about0.30 or more (e.g., at least about 0.40). Even higher fillingcoefficients are possible in buffer tubes containing bend-insensitivefibers. For example, such buffer tubes typically have a buffer-tubesfilling coefficient of greater than 0.50, more typically at least about0.60 (e.g., 0.70 or more). In this regard, buffer tubes in accordancewith the present invention typically include between 12 and 432 opticalfibers (e.g., 216 optical fibers configured as a 12×18 ribbon stack).That said, buffer tubes having higher fiber counts (e.g., at least 864optical fibers) are within the scope of the present invention.

Optical-fiber cables containing the present water-blocking elementstypically demonstrate exceptional resistance to attenuation asdetermined by temperature cycle testing, even though these cablestypically possess relatively high buffer-tube filling coefficients. Forexample, optical-fiber cables in accordance with the present inventionmeet or exceed temperature cycling requirements as set forth inGR-20-CORE (6.6.3, Issue 3, May. 2008), hereinafter referred to as the“GR-20-CORE temperature cycling requirement.” The GR-20-CORE temperaturecycling requirement is hereby incorporated by reference in its entirety.

Moreover, optical-fiber cables containing the present water-blockingelements typically demonstrate exceptional resistance to waterpenetration as determined by water-penetration testing. For example,optical-fiber cables in accordance with the present invention meet orexceed water-penetration requirements as set forth in GR-20-CORE (6.6.7,Issue 3, May. 2008), hereinafter referred to as the “GR-20-COREwater-penetration requirement.” The GR-20-CORE water-penetrationrequirement is hereby incorporated by reference in its entirety.

The optical-fiber cables according to the present invention may alsomeet or exceed certain Telcordia Technologies generic requirements foroptical-fiber cables as set forth in GR-20-CORE (Issue 2, July. 1998;Issue 3, May. 2008), such as low-temperature and high-temperature cablebend (6.5.3), impact resistance (6.5.4), compression (6.5.5), tensilestrength of cable (6.5.6), cable twist (6.5.7), cable cyclic flexing(6.5.8), mid-span buffer tube performance of stranded cable (6.5.11),cable aging (6.6.4), and cable freezing (6.6.5). These GR-20-COREgeneric requirements (i.e., Issue 2, July 1998, and Issue 3, May 2008,respectively) are hereby incorporated by reference in their entirety.

* * *

The water-blocking elements according to the present invention may bedeployed in various structures, such as those exemplary structuresdisclosed hereinafter.

As noted, one or more of the present water-blocking elements may beenclosed within a buffer tube. For instance, one or more water-blockingelements may be deployed in either a single fiber loose buffer tube or amulti-fiber loose buffer tube. With respect to the latter, multipleoptical fibers may be bundled or stranded within a buffer tube or otherstructure. In this regard, within a multi-fiber loose buffer tube, fibersub-bundles may be separated with binders (e.g., each fiber sub-bundleis enveloped in a binder). Moreover, fan-out tubing may be installed atthe termination of such loose buffer tubes to directly terminate loosebuffered optical fibers with field-installed connectors.

Such buffer tubes may contain conventional glass fibers orbend-insensitive glass fibers. An exemplary bend-insensitive glass fiberfor use in the present invention is disclosed in U.S. Pat. No. 7,623,747for a Single Mode Optical Fiber.

With respect to conventional and bend-insensitive optical fibers, thecomponent glass fiber typically has an outer diameter of about 125microns. With respect to an optical fiber's surrounding coating layers,the primary coating typically has an outer diameter of between about 175microns and about 195 microns (i.e., a primary coating thickness ofbetween about 25 microns and 35 microns) and the secondary coatingtypically has an outer diameter of between about 235 microns and about265 microns (i.e., a secondary coating thickness of between about 20microns and 45 microns). Optionally, the optical fiber may include anoutermost ink layer, which is typically between two and ten microns inthickness.

In one alternative embodiment, an optical fiber may possess a reduceddiameter (e.g., an outermost diameter between about 150 microns and 230microns). In this alternative optical fiber configuration, the thicknessof the primary coating and/or secondary coating is reduced, while thediameter of the component glass fiber is maintained at about 125microns. (Those having ordinary skill in the art will appreciate that,unless otherwise specified, diameter measurements refer to outerdiameters.)

By way of illustration, in such exemplary embodiments the primarycoating layer may have an outer diameter of between about 135 micronsand about 175 microns (e.g., about 160 microns), typically less than 165microns (e.g., between about 135 microns and 150 microns) and usuallymore than 140 microns (e.g., between about 145 microns and 155 microns,such as about 150 microns).

Moreover, in such exemplary embodiments the secondary coating layer mayhave an outer diameter of between about 150 microns and about 230microns (e.g., more than about 165 microns, such as 190-210 microns orso), typically between about 180 microns and 200 microns. In otherwords, the total diameter of the optical fiber is reduced to less thanabout 230 microns (e.g., between about 195 microns and 205 microns, andespecially about 200 microns). By way of further illustration, anoptical fiber may employ a secondary coating of about 197 microns at atolerance of +/− 5 microns (i.e., a secondary-coating outer diameter ofbetween 192 microns to 202 microns). Typically, the secondary coatingwill retain a thickness of at least about 10 microns (e.g., an opticalfiber having a reduced thickness secondary coating of between 15 micronsand 25 microns).

In another alternative embodiment, the outer diameter of the componentglass fiber may be reduced to less than 125 microns (e.g., between about60 microns and 120 microns), perhaps between about 70 microns and 115microns (e.g., about 80-110 microns). This may be achieved, forinstance, by reducing the thickness of one or more cladding layers. Ascompared with the prior alternative embodiment, (i) the total diameterof the optical fiber may be reduced (i.e., the thickness of the primaryand secondary coatings are maintained in accordance with the prioralternative embodiment) or (ii) the respective thicknesses of theprimary and/or secondary coatings may be increased relative to the prioralternative embodiment (e.g., such that the total diameter of theoptical fiber might be maintained).

By way of illustration, with respect to the former, a component glassfiber having a diameter of between about 90 and 100 microns might becombined with a primary coating layer having an outer diameter ofbetween about 110 microns and 150 microns (e.g., about 125 microns) anda secondary coating layer having an outer diameter of between about 130microns and 190 microns (e.g., about 155 microns). With respect to thelatter, a component glass fiber having a diameter of between about 90and 100 microns might be combined with a primary coating layer having anouter diameter of between about 120 microns and 140 microns (e.g., about130 microns) and a secondary coating layer having an outer diameter ofbetween about 160 microns and 230 microns (e.g., about 195-200 microns).

Reducing the diameter of the component glass fiber might make theresulting optical fiber more susceptible to microbending attenuation.That said, the advantages of further reducing optical-fiber diameter maybe worthwhile for some optical-fiber applications.

As noted, optical fibers contained within buffer tubes and cables inaccordance with the present invention typically include one or morecoating layers (e.g., a primary coating and a secondary coating). Atleast one of the coating layers—typically the secondary coating—may becolored and/or possess other markings to help identify individualfibers. Alternatively, a tertiary ink layer may surround the primary andsecondary coatings.

Such fibers may include a low-modulus primary coating for reducing therisk of microbending. A low-modulus primary coating can be combined withbend-insensitive fiber for providing unexpectedly superior reductions inmicrobend sensitivity.

As will be known by those having ordinary skill in the art, an exemplarybuffer tube enclosing water-blocking elements as disclosed herein may beformed of polyolefins (e.g., polyethylene or polypropylene), includingfluorinated polyolefins, polyesters (e.g., polybutylene terephthalate),polyamides (e.g., nylon), as well as other polymeric materials andblends. In general, a buffer tube may be formed of one or more layers.The layers may be homogeneous or include mixtures or blends of variousmaterials within each layer.

In this context, the buffer tube may be extruded (e.g., an extrudedpolymeric material) or pultruded (e.g., a pultruded, fiber-reinforcedplastic). By way of example, the buffer tube may include a material toprovide high temperature and chemical resistance (e.g., an aromaticmaterial or polysulfone material).

Although buffer tubes typically have a circular cross section, buffertubes alternatively may have an irregular or non-circular shape (e.g.,an oval or a trapezoidal cross-section).

Alternatively, one or more of the present water-blocking elements may becontained within structures such as a metal tube or an outer protectivesheath encapsulating one or more optical fibers. In either structure, nointermediate buffer tube is necessarily required.

Multiple optical fibers may be sandwiched, encapsulated, and/or edgebonded to form an optical-fiber ribbon. Optical-fiber ribbons can bedivisible into subunits (e.g., a twelve-fiber ribbon that is splittableinto six-fiber subunits). Moreover, a plurality of such optical-fiberribbons may be aggregated to form a ribbon stack, which can have varioussizes and shapes.

For example, it is possible to form a rectangular ribbon stack or aribbon stack in which the uppermost and lowermost optical-fiber ribbonshave fewer optical fibers than those toward the center of the stack.This construction may be useful to increase the density of opticalelements (e.g., optical fibers) within the buffer tube and/or cable.

In general, it is desirable to increase the filling of transmissionelements in buffer tubes or cables, subject to other constraints (e.g.,cable or mid-span attenuation). The optical elements themselves may bedesigned for increased packing density. For example, the optical fibermay possess modified properties, such as improved refractive-indexprofile, core or cladding dimensions, or primary coating thicknessand/or modulus, to improve microbending and macrobendingcharacteristics.

By way of example, a rectangular ribbon stack may be formed with orwithout a central twist (i.e., a “primary twist”). Those having ordinaryskill in the art will appreciate that a ribbon stack is typicallymanufactured with rotational twist to allow the tube or cable to bendwithout placing excessive mechanical stress on the optical fibers duringwinding, installation, and use. In a structural variation, a twisted (oruntwisted) rectangular ribbon stack may be further formed into acoil-like configuration (e.g., a helix) or a wave-like configuration(e.g., a sinusoid). In other words, the ribbon stack may possess regular“secondary” deformations.

As will be known to those having ordinary skill in the art, suchoptical-fiber ribbons may be positioned within a buffer tube or othersurrounding structure, such as a buffer-tube-free cable, that containwater-blocking elements according to the present invention. Subject tocertain restraints (e.g., attenuation) it is desirable to increase thedensity of elements such as optical fibers or optical-fiber ribbonswithin buffer tubes and/or optical-fiber cables.

A plurality of buffer tubes containing optical fibers (e.g., loose orribbonized fibers) may be positioned externally adjacent to and strandedaround a central strength member. This stranding can be accomplished inone direction, helically, known as “S” or “Z” stranding, or ReverseOscillated Lay stranding, known as “S-Z” stranding. Stranding about thecentral strength member reduces optical-fiber strain when cable strainoccurs during installation and use.

Those having ordinary skill in the art will understand the benefit ofminimizing fiber strain for both tensile cable strain and longitudinalcompressive cable strain during installation or operating conditions.

With respect to tensile cable strain, which may occur duringinstallation, the cable will become longer while the optical fibers canmigrate closer to the cable's neutral axis to reduce, if not eliminate,the strain being translated to the optical fibers. With respect tolongitudinal compressive strain, which may occur at low operatingtemperatures due to shrinkage of the cable components, the opticalfibers will migrate farther away from the cable's neutral axis toreduce, if not eliminate, the compressive strain being translated to theoptical fibers.

In a variation, two or more substantially concentric layers of buffertubes may be positioned around a central strength member. In a furthervariation, multiple stranding elements (e.g., multiple buffer tubesstranded around a strength member) may themselves be stranded aroundeach other or around a primary central strength member.

Alternatively, a plurality of buffer tubes containing optical fibers(e.g., loose or ribbonized fibers) may be simply placed externallyadjacent to the central strength member (i.e., the buffer tubes are notintentionally stranded or arranged around the central strength member ina particular manner and run substantially parallel to the centralstrength member).

Alternatively still, the present water-blocking elements may bepositioned within a central buffer tube (i.e., the central buffer tubecable has a central buffer tube rather than a central strength member).Such a central buffer tube cable may position strength memberselsewhere. For instance, metallic or non-metallic (e.g., GRP) strengthmembers may be positioned within the cable sheath itself, and/or one ormore layers of high-strength yarns (e.g., aramid or non-aramid yarns)may be positioned parallel to or wrapped (e.g., contrahelically) aroundthe central buffer tube (i.e., within the cable's interior space).Likewise, strength members can be included within the buffer tube'scasing.

In other embodiments, the water-blocking elements according to thepresent invention may be placed within a slotted core cable. In aslotted core cable, optical fibers, individually or as a fiber ribbon,may be placed within pre-shaped helical grooves (i.e., channels) on thesurface of a central strength member, thereby forming a slotted coreunit. The slotted core unit may be enclosed by a buffer tube. One ormore of such slotted core units may be placed within a slotted corecable. For example, a plurality of slotted core units may be helicallystranded around a central strength member.

Alternatively, the optical fibers may also be stranded in a maxitubecable design, whereby the optical fibers are stranded around themselveswithin a large multi-fiber loose buffer tube rather than around acentral strength member. In other words, the large multi-fiber loosebuffer tube is centrally positioned within the maxitube cable. Forexample, such maxitube cables may be deployed in optical ground wires(OPGW).

In another cabling embodiment, multiple buffer tubes may be strandedaround themselves without the presence of a central member. Thesestranded buffer tubes may be surrounded by a protective tube. Theprotective tube may serve as the outer casing of the fiber optic cableor may be further surrounded by an outer sheath. The protective tube maytightly or loosely surround the stranded buffer tubes.

As will be known to those having ordinary skill in the art, additionalelements may be included within a cable core. For example, copper cablesor other active, transmission elements may be stranded or otherwisebundled within the cable sheath. Passive elements may also be placedwithin the cable core, such as between the interior walls of the buffertubes and the enclosed optical fibers. Alternatively and by way ofexample, passive elements may be placed outside the buffer tubes betweenthe respective exterior walls of the buffer tubes and the interior wallof the cable jacket, or, within the interior space of a buffer-tube-freecable.

Moreover, an adhesive (e.g., a hot-melt adhesive or curable adhesive,such as a silicone acrylate cross-linked by exposure to actinicradiation) may be provided on one or more passive elements (e.g.,water-swellable material) to bond the elements to the buffer tube. Anadhesive material may also be used to bond the water-swellable elementto optical fibers within the buffer tube. Exemplary arrangements of suchelements are disclosed in commonly assigned U.S. Pat. No. 7,515,795 fora Water-Swellable Tape, Adhesive-Backed for Coupling When Used Inside aBuffer Tube and commonly assigned U.S. Pat. No. 7,599,589 for a Gel-FreeBuffer Tube with Adhesively Coupled Optical Element, each of which ishereby incorporated by reference in its entirety.

As will be understood by those having ordinary skill in the art, a cableenclosing water-blocking elements as disclosed herein may have a sheathformed from various materials in various designs. Cable sheathing may beformed from polymeric materials such as, for example, polyethylene,polypropylene, polyvinyl chloride (PVC), polyamides (e.g., nylon),polyester (e.g., PBT), fluorinated plastics (e.g., perfluorethylenepropylene, polyvinyl fluoride, or polyvinylidene difluoride), andethylene vinyl acetate. The sheath and/or buffer tube materials may alsocontain other additives, such as nucleating agents, flame-retardants,smoke-retardants, antioxidants, UV absorbers, and/or plasticizers.

The cable sheathing may be a single jacket formed from a dielectricmaterial (e.g., non-conducting polymers), with or without supplementalstructural components that may be used to improve the protection (e.g.,from rodents) and strength provided by the cable sheath. For example,one or more layers of metallic (e.g., steel) tape along with one or moredielectric jackets may form the cable sheathing. Metallic or fiberglassreinforcing rods (e.g., GRP) may also be incorporated into the sheath.In addition, aramid, fiberglass, or polyester yarns may be employedunder the various sheath materials (e.g., between the cable sheath andthe cable core), and/or ripcords may be positioned, for example, withinthe cable sheath.

Similar to buffer tubes, optical-fiber cable sheaths typically have acircular cross section, but cable sheaths alternatively may have anirregular or non-circular shape (e.g., an oval, trapezoidal, or flatcross-section).

By way of example, the water blocking elements according to the presentinvention may be incorporated into single-fiber drop cables, such asthose employed for Multiple Dwelling Unit (MDU) applications. In suchdeployments, the cable jacketing must exhibit crush resistance, abrasionresistance, puncture resistance, thermal stability, and fire resistanceas required by building codes. An exemplary material for such cablejackets is thermally stable, flame-retardant polyurethane (PUR), whichmechanically protects the optical fibers yet is sufficiently flexible tofacilitate easy MDU installations. Alternatively, a flame-retardantpolyolefin or polyvinyl chloride sheath may be used.

In general and as will be known to those having ordinary skill in theart, a strength member is typically in the form of a rod orbraided/helically wound wires or fibers, though other configurationswill be within the knowledge of those having ordinary skill in the art.

Optical-fiber cables containing water-blocking elements as disclosed maybe variously deployed, including as drop cables, distribution cables,feeder cables, trunk cables, and stub cables, each of which may havevarying operational requirements (e.g., temperature range, crushresistance, UV resistance, and minimum bend radius).

Such optical-fiber cables may be installed within ducts, microducts,plenums, or risers. By way of example, an optical-fiber cable may beinstalled in an existing duct or microduct by pulling or blowing (e.g.,using compressed air). An exemplary cable installation method isdisclosed in commonly assigned U.S. Pat. No. 7,574,095 for aCommunication Cable Assembly and Installation Method, (Lock et al.), andU.S. Patent Application Publication No. 2008/0317410 for a ModifiedPre-Ferrulized Communication Cable Assembly and Installation Method,(Griffioen et al.), each of which is incorporated by reference in itsentirety.

As noted, buffer tubes containing optical fibers (e.g., loose orribbonized fibers) may be stranded (e.g., around a central strengthmember). In such configurations, an optical-fiber cable's protectiveouter sheath may have a textured outer surface that periodically varieslengthwise along the cable in a manner that replicates the strandedshape of the underlying buffer tubes. The textured profile of theprotective outer sheath can improve the blowing performance of theoptical-fiber cable. The textured surface reduces the contact surfacebetween the cable and the duct or microduct and increases the frictionbetween the blowing medium (e.g., air) and the cable. The protectiveouter sheath may be made of a low coefficient-of-friction material,which can facilitate blown installation. Moreover, the protective outersheath can be provided with a lubricant to further facilitate blowninstallation.

In general, to achieve satisfactory long-distance blowing performance(e.g., between about 3,000 to 5,000 feet or more), the outer cablediameter of an optical-fiber cable should be no more than about 70 to 80percent of the duct's or microduct's inner diameter.

Compressed air may also be used to install optical fibers in an airblown fiber system. In an air blown fiber system, a network of unfilledcables or microducts is installed prior to the installation of opticalfibers. Optical fibers may subsequently be blown into the installedcables as necessary to support the network's varying requirements.

Moreover, the optical-fiber cables may be directly buried in the groundor, as an aerial cable, suspended from a pole or pylon. An aerial cablemay be self-supporting or secured or lashed to a support (e.g.,messenger wire or another cable). Exemplary aerial fiber optic cablesinclude overhead ground wires (OPGW), all-dielectric self-supportingcables (ADSS), all dielectric lash cables (AD-Lash), and figure-eightcables, each of which is well understood by those having ordinary skillin the art. Figure-eight cables and other designs can be directly buriedor installed into ducts, and may optionally include a toning element,such as a metallic wire, so that they can be found with a metaldetector.

In addition, although the optical fibers may be further protected by anouter cable sheath, the optical fiber itself may be further reinforcedso that the optical fiber may be included within a breakout cable, whichallows for the individual routing of individual optical fibers.

To effectively employ optical fibers in a transmission system,connections are required at various points in the network. Optical-fiberconnections are typically made by fusion splicing, mechanical splicing,or mechanical connectors.

The mating ends of connectors can be installed to the fiber ends eitherin the field (e.g., at the network location) or in a factory prior toinstallation into the network. The ends of the connectors are mated inthe field in order to connect the fibers together or connect the fibersto the passive or active components. For example, certain optical-fibercable assemblies (e.g., furcation assemblies) can separate and conveyindividual optical fibers from a multiple optical-fiber cable toconnectors in a protective manner.

The deployment of such optical-fiber cables may include supplementalequipment. For instance, an amplifier may be included to improve opticalsignals. Dispersion compensating modules may be installed to reduce theeffects of chromatic dispersion and polarization mode dispersion. Spliceboxes, pedestals, and distribution frames, which may be protected by anenclosure, may likewise be included. Additional elements include, forexample, remote terminal switches, optical network units, opticalsplitters, and central office switches.

A cable containing water-blocking elements according to the presentinvention may be deployed for use in a communication system (e.g.,networking or telecommunications). A communication system may includefiber optic cable architecture such as fiber-to-the-node (FTTN),fiber-to-the-telecommunications enclosure (FTTE), fiber-to-the-curb(FITC), fiber-to-the-building (FTTB), and fiber-to-the-home (FTTH), aswell as long-haul or metro architecture. Moreover, an optical module ora storage box that includes a housing may receive a wound portion of theoptical fiber disclosed herein. By way of example, the optical fiber maybe wound with a bending radius of less than about 15 millimeters (e.g.,10 millimeters or less, such as about 5 millimeters) in the opticalmodule or the storage box.

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To supplement the present disclosure, this application incorporatesentirely by reference the following commonly assigned patents, patentapplication publications, and patent applications: U.S. Pat. No.4,838,643 for a Single Mode Bend Insensitive Fiber for Use in FiberOptic Guidance Applications (Hodges et al.); U.S. Pat. No. 7,623,747 fora Single Mode Optical Fiber (de Montmorillon et al.); U.S. Pat. No.7,587,111 for a Single-Mode Optical Fiber (de Montmorillon et al.); U.S.Pat. No. 7,356,234 for a Chromatic Dispersion Compensating Fiber (deMontmorillon et al.); U.S. Pat. No. 7,483,613 for a Chromatic DispersionCompensating Fiber (de Montmorillon et al.); U.S. Pat. No. 7,555,186 foran Optical Fiber (Flammer et al.); U.S. Patent Application PublicationNo. US2009/0252469 A1 for a Dispersion-Shifted Optical Fiber (Sillard etal.); U.S. patent application Ser. No. 12/098,804 for a TransmissionOptical Fiber Having Large Effective Area (Sillard et al.), filed Apr.7, 2008; International Patent Application Publication No. WO 2009/062131A1 for a Microbend-Resistant Optical Fiber, (Overton); U.S. PatentApplication Publication No. US2009/0175583 A1 for a Microbend-ResistantOptical Fiber, (Overton); U.S. Patent Application Publication No.US2009/0279835 A1 for a Single-Mode Optical Fiber Having Reduced BendingLosses, filed May. 6, 2009, (de Montmorillon et al.); U.S. PatentApplication Publication No. US2009/0279836 A1 for a Bend-InsensitiveSingle-Mode Optical Fiber, filed May. 6, 2009, (de Montmorillon et al.);U.S. patent application Ser. No. 12/489,995 for a Wavelength MultiplexedOptical System with Multimode Optical Fibers, filed Jun. 23, 2009,(Lumineau et al.); U.S. patent application Ser. No. 12/498,439 for aMultimode Optical Fibers, filed Jul. 7, 2009, (Gholami et al.); U.S.patent application Ser. No. 12/614,011 for a Reduced-Diameter OpticalFiber, filed Nov. 6, 2009, (Overton); U.S. Pat. application Ser. No.12/614,172 for a Multimode Optical System, filed Nov. 6, 2009, (Gholamiet al.); U.S. patent application Ser. No. 12/617,316 for an AmplifyingOptical Fiber and Method of Manufacturing, filed Nov. 12, 2009,(Pastouret et al.) U.S. patent application Ser. No. 12/629,495 for anAmplifying Optical Fiber and Production Method, filed Dec. 2, 2009,(Pastouret et al.); U.S. patent application Ser. No. 12/633,229 for anIonizing Radiation-Resistant Optical Fiber Amplifier, filed Dec. 8,2009, (Regnier et al.); and U.S. patent application Ser. No. 12/636,277for a Buffered Optical Fiber, filed Dec. 11, 2009, (Testu et al.).

To supplement the present disclosure, this application furtherincorporates entirely by reference the following commonly assignedpatents, patent application publications, and patent applications: U.S.Pat. No. 5,574,816 for Polypropylene-Polyethylene Copolymer Buffer Tubesfor Optical Fiber Cables and Method for Making the Same; U.S. Pat. No.5,717,805 for Stress Concentrations in an Optical Fiber Ribbon toFacilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 5,761,362for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical FiberCables and Method for Making the Same; U.S. Pat. No. 5,911,023 forPolyolefin Materials Suitable for Optical Fiber Cable Components; U.S.Pat. No. 5,982,968 for Stress Concentrations in an Optical Fiber Ribbonto Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No.6,035,087 for an Optical Unit for Fiber Optic Cables; U.S. Pat. No.6,066,397 for Polypropylene Filler Rods for Optical Fiber CommunicationsCables; U.S. Pat. No. 6,175,677 for an Optical Fiber Multi-Ribbon andMethod for Making the Same; U.S. Pat. No. 6,085,009 for Water BlockingGels Compatible with Polyolefin Optical Fiber Cable Buffer Tubes andCables Made Therewith; U.S. Pat. No. 6,215,931 for FlexibleThermoplastic Polyolefin Elastomers for Buffering Transmission Elementsin a Telecommunications Cable; U.S. Pat. No. 6,134,363 for a Method forAccessing Optical Fibers in the Midspan Region of an Optical FiberCable; U.S. Pat. No. 6,381,390 for a Color-Coded Optical Fiber Ribbonand Die for Making the Same; U.S. Pat. No. 6,181,857 for a Method forAccessing Optical Fibers Contained in a Sheath; U.S. Pat. No. 6,314,224for a Thick-Walled Cable Jacket with Non-Circular Cavity Cross Section;U.S. Pat. No. 6,334,016 for an Optical Fiber Ribbon Matrix MaterialHaving Optimal Handling Characteristics; U.S. Pat. No. 6,321,012 for anOptical Fiber Having Water Swellable Material for Identifying Groupingof Fiber Groups; U.S. Pat. No. 6,321,014 for a Method for ManufacturingOptical Fiber Ribbon; U.S. Pat. No. 6,210,802 for Polypropylene FillerRods for Optical Fiber Communications Cables; U.S. Pat. No. 6,493,491for an Optical Drop Cable for Aerial Installation; U.S. Pat. No.7,346,244 for a Coated Central Strength Member for Fiber Optic Cableswith Reduced Shrinkage; U.S. Pat. No. 6,658,184 for a Protective Skinfor Optical Fibers; U.S. Pat. No. 6,603,908 for a Buffer Tube thatResults in Easy Access to and Low Attenuation of Fibers Disposed WithinBuffer Tube; U.S. Pat. No. 7,045,010 for an Applicator for High-SpeedGel Buffering of Flextube Optical Fiber Bundles; U.S. Pat. No. 6,749,446for an Optical Fiber Cable with Cushion Members Protecting Optical FiberRibbon Stack; U.S. Pat. No. 6,922,515 for a Method and Apparatus toReduce Variation of Excess Fiber Length in Buffer Tubes of Fiber OpticCables; U.S. Pat. No. 6,618,538 for a Method and Apparatus to ReduceVariation of Excess Fiber Length in Buffer Tubes of Fiber Optic Cables;U.S. Pat. No. 7,322,122 for a Method and Apparatus for Curing a FiberHaving at Least Two Fiber Coating Curing Stages; U.S. Pat. No. 6,912,347for an Optimized Fiber Optic Cable Suitable for Microduct BlownInstallation; U.S. Pat. No. 6,941,049 for a Fiber Optic Cable Having NoRigid Strength Members and a Reduced Coefficient of Thermal Expansion;U.S. Pat. No. 7,162,128 for Use of Buffer Tube Coupling Coil to PreventFiber Retraction; U.S. Pat. No. 7,515,795 for a Water-Swellable Tape,Adhesive-Backed for Coupling When Used Inside a Buffer Tube (Overton etal.); U.S. Patent Application Publication No. 2008/0292262 for aGrease-Free Buffer Optical Fiber Buffer Tube Construction Utilizing aWater-Swellable, Texturized Yarn (Overton et al.); European PatentApplication Publication No. 1,921,478 A1, for a TelecommunicationOptical Fiber Cable (Tatat et al.); U.S. Pat. No. 7,570,852 for anOptical Fiber Cable Suited for Blown Installation or PushingInstallation in Microducts of Small Diameter (Nothofer et al.); U.S.Patent Application Publication No. US 2008/0037942 A1 for an OpticalFiber Telecommunications Cable (Tatat); U.S. Pat. No. 7,599,589 for aGel-Free Buffer Tube with Adhesively Coupled Optical Element (Overton etal.); U.S. Pat. No. 7,567,739 for a Fiber Optic Cable Having aWater-Swellable Element (Overton); U.S. Patent Application PublicationNo. US2009/0041414 A1 for a Method for Accessing Optical Fibers within aTelecommunication Cable (Lavenne et al.); U.S. Patent ApplicationPublication No. US2009/0003781 A1 for an Optical Fiber Cable Having aDeformable Coupling Element (Parris et al.); U.S. Patent ApplicationPublication No. US2009/0003779 A1 for an Optical Fiber Cable HavingRaised Coupling Supports (Parris); U.S. Patent Application PublicationNo. US2009/0003785 A1 for a Coupling Composition for Optical FiberCables (Parris et al.); U.S. Patent Application Publication No.US2009/0214167 A1 for a Buffer Tube with Hollow Channels, (Lookadoo etal.); U.S. patent application Ser. No. 12/466,965 for an Optical FiberTelecommunication Cable, filed May 15, 2009, (Tatat); U.S. patentapplication Ser. No. 12/506,533 for a Buffer Tube with AdhesivelyCoupled Optical Fibers and/or Water-Swellable Element, filed Jul. 21,2009, (Overton et al.); U.S. patent application Ser. No. 12/557,055 foran Optical Fiber Cable Assembly, filed Sep. 10, 2009, (Barker et al.);U.S. patent application Ser. No. 12/557,086 for a High-Fiber-DensityOptical Fiber Cable, filed Sep. 10, 2009, (Louie et al.); U.S. patentapplication Ser. No. 12/558,390 for a Buffer Tubes for Mid-Span Storage,filed Sep. 11, 2009, (Barker); U.S. patent application Ser. No.12/614,692 for Single-Fiber Drop Cables for MDU Deployments, filed Nov.9, 2009, (Overton); U.S. patent application Ser. No. 12/614,754 forOptical-Fiber Loose Tube Cables, filed Nov. 9, 2009, (Overton); U.S.patent application Ser. No. 12/615,003 for a Reduced-Size Flat DropCable, filed Nov. 9, 2009, (Overton et al.); U.S. patent applicationSer. No. 12/615,106 for ADSS Cables with High-Performance Optical Fiber,filed Nov. 9, 2009, (Overton); U.S. patent application Ser. No.12/615,698 for Reduced-Diameter Ribbon Cables with High-PerformanceOptical Fiber, filed Nov. 10, 2009, (Overton); U.S. patent applicationSer. No. 12/615,737 for a Reduced-Diameter, Easy-Access Loose TubeCable, filed Nov. 10, 2009, (Overton); and U.S. patent application No.12/642,784 for a Method and Device for Manufacturing an Optical Preform,filed Dec. 19, 2009, (Milicevic et al.).

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In the specification and/or figures, typical embodiments of theinvention have been disclosed. The present invention is not limited tosuch exemplary embodiments. The figures are schematic representationsand so are not necessarily drawn to scale. Unless otherwise noted,specific terms have been used in a generic and descriptive sense and notfor purposes of limitation.

The invention claimed is:
 1. An optical-fiber cable, comprising: anoptical fiber; a buffer tube enclosing said optical fiber; awater-blocking element positioned between said optical fiber and saidbuffer tube, said water-blocking element comprising (i) a fibrouscarrier tape defining a plurality of discrete perforations and (ii) awater-swellable particulate powder bonded to said perforated fibrouscarrier tape, wherein said water-blocking element at least partiallysurrounds said optical fiber and wherein said perforated fibrous carriertape is positioned adjacent to said optical fiber and saidwater-swellable powder is positioned opposite said optical fiber; and apolymeric cable jacket surrounding said buffer tube.
 2. Theoptical-fiber cable according to claim 1, wherein: said buffer tubeencloses a plurality of optical fibers, said buffer tube possessing afilling coefficient of at least about 0.20; and the optical-fiber cablecomplies with the GR-20-CORE temperature cycling requirement.
 3. Theoptical-fiber cable according to claim 2, wherein: said buffer tubeencloses a plurality of bend-insensitive optical fibers, said buffertube possessing a filling coefficient of at least about 0.50; and theoptical-fiber cable complies with the GR-20-CORE temperature cyclingrequirement.
 4. The optical-fiber cable according to claim 1, whereinsaid perforated fibrous carrier tape possesses Shore A hardness of morethan about
 25. 5. The optical-fiber cable according to claim 1, whereinsaid perforated fibrous carrier tape possesses Shore A hardness of morethan about
 45. 6. The optical-fiber cable according to claim 1, whereinsaid perforated fibrous carrier tape is a water-insoluble carrier tapethat maintains its strength and structural integrity when immersed inwater.
 7. The optical-fiber cable according to claim 1, wherein theplurality of perforations defined by said perforated fibrous carriertape are sized to hinder the dry migration of said water-swellableparticulate powder through said perforated fibrous carrier tape.
 8. Theoptical-fiber cable according to claim 1, wherein said perforatedfibrous carrier tape comprises a substrate formed from a plurality ofpolymeric fibers, wherein the density of said substrate is at leastabout 80 percent of the density of said polymeric fibers.
 9. Theoptical-fiber cable according to claim 1, wherein said perforatedfibrous carrier tape comprises a substrate formed from a plurality ofpolymeric fibers, wherein the density of said substrate is at leastabout 90 percent of the density of said polymeric fibers.
 10. Theoptical-fiber cable according to claim 1, wherein said perforatedfibrous carrier tape comprises natural fibers.
 11. The optical-fibercable according to claim 1, wherein said perforated fibrous carrier tapecomprises paper.
 12. The optical-fiber cable according to claim 1,wherein said perforated fibrous carrier tape comprises parchment paper.13. The optical-fiber cable according to claim 1, comprising an adhesivematerial bonding said optical fiber to said water-blocking element. 14.The optical-fiber cable according to claim 13, wherein said adhesivematerial is discontinuously provided on said perforated carrier tape.15. The optical-fiber cable according to claim 13, wherein said adhesivematerial bonds said water-blocking element to said buffer tube.
 16. Anoptical-fiber cable, comprising: an optical fiber; a buffer tubeenclosing said optical fiber; a water-blocking element positionedbetween said optical fiber and said buffer tube, said water-blockingelement comprising (i) first and second fibrous carrier tapes, each ofsaid first and second carrier tapes defining a plurality of perforationsand interstices that facilitate the passage of water and (ii) awater-swellable particulate powder disposed between said first andsecond carrier tapes, wherein said water-blocking element at leastpartially surrounds said optical fiber; and a polymeric cable jacketsurrounding said buffer tube.
 17. The optical-fiber cable according toclaim 16, wherein: said buffer tube encloses a plurality of opticalfibers, said buffer tube possessing a filling coefficient of at leastabout 0.30; and the optical-fiber cable complies with the GR-20-COREtemperature cycling requirement.
 18. The optical-fiber cable accordingto claim 16, wherein said first and second carrier tapes arewater-insoluble carrier tapes that maintain their strength andstructural integrity when immersed in water.
 19. The optical-fiber cableaccording to claim 16, wherein said first and second carrier tapescomprise a substrate formed from a plurality of polymeric fibers,wherein the density of said substrate is at least about 80 percent ofthe density of said polymeric fibers.
 20. The optical-fiber cableaccording to claim 16, wherein said first and second carrier tapes areformed from a plurality of natural fibers.
 21. The optical-fiber cableaccording to claim 16, comprising an adhesive material bonding saidoptical fiber to said water-blocking element.
 22. The optical-fibercable according to claim 16, wherein said water-blocking element is athree-layer structure in which said water-swellable particulate powderis encapsulated between said first and second carrier tapes.
 23. Theoptical-fiber cable according to claim 1, wherein said water-blockingelement is a two-layer structure in which said water-swellableparticulate powder is bonded to said perforated fibrous carrier tape.